The purpose of this program is to investigate the role of immune complexes and immunogenetic factors in patients with rheumatic diseases. Studies on immune complexes will focus on: the ability of isolated antigen-antibody complexes, with or without complement, to react in different immune complex assays: the ability of immune complexes to bind to normal cells of the reticuloendothelial system; whether cells of the reticuloendothelial system in patients with rheumatic diseases are defective in their ability to bind immune complexes; and to determine the relationship between immune complexes and cells and clinical and pathological features of patients with rheumatic diseases. Studies on immunogenetics will focus on: determining the frequency of immunoglobulin and complement deficiencies and B lymphocyte (Ia) antigens in patients with rheumatic diseases; determination whether these deficiencies and B lymphocyte antigens are linked to HLA or other genetic markers; to investigate serum IgD deficiency; to determine the relationship between HLA haplotypes and disease in families with rheumatic disease; to determine the frequency of crossovers on the sixth crossover in such patients; and to determine whether genetic markers identify a clinical or immunological subset of patients with either systemic lupus erythematosus, rheumatoid arthritis, juvenile rheumatoid arthritis, vasculitis, or psoriatic arthritis.